About 10 to 30% of ataxia-telangiectasia (A-T) patients develop leukemias or lymphomas. There is considerable interpatient variation in the age of onset and leukemia/lymphoma type. The incomplete penetrance and variable age of onset may be attributable to several factors. These include competing mortality from neurodegeneration and interstitial lung disease, and allele specific effects of ATM gene mutations. Also, there is limited evidence from clinical observations and studies using Atm knockout mice that modifier genes may account for some variation in leukemia/lymphoma susceptibility. We have introgressed the Atmtm1Awb knockout allele (Atm-) onto several inbred murine strains and observed differences in survival between Atm-/- mice on the different strain backgrounds. The primary aim of this proposal is to characterize the incidence and onset latency of thymic lymphoma in these Atm-/- congenic strains as a prelude to identifying lymphomagenesis modifier genes. A secondary aim is to assay aged Atm-/- mice for neurodegeneration and interstitial lung disease, since these clinically important phenotypes are not recapitulated in existing Atm knockout mouse strains. PUBLIC HEALTH RELEVELANCE: The major causes of death in ataxia-telangiectasia (A-T) patients are interstitial lung disease and cancer, specifically leukemias and lymphomas. This project aims to characterize a potential animal model for A-T that can be used to determine why some patients get leukemia and others don't. The model may also be useful for the testing of potential therapies against interstitial lung disease and neurodegeneration in A-T patients.